This invention relates to a method for detecting an abnormality in the functioning of an electronic control system, and more particularly to a method of this kind which can perform such abnormality determination in an accurate manner without making a wrong diagnosis.
An abnormality detecting method has conventionally been employed, which comprises detecting abnormalities in the functioning of input means and output means of an electronic control system, particularly one for controlling the operation of an internal combustion engine, such as an electronic fuel supply control system, an ignition timing control system, an exhaust gas recirculation control system, an idling speed control system, and an air-fuel ratio feedback control system, and upon detection of such an abnormality, performing a warning action and/or a fail-safe action, thereby preventing malfunction of the engine even in the event of a failure in such input means or output means.
The above input means typically include various sensors for detecting values of various operating parameters of an internal combustion engine, such as engine rotational speed, throttle valve opening and exhaust gas concentration, and values of parameters indicative of atmospheric conditions such as atmospheric pressure and ambient temperature, analog-to-digital converters for converting the detected parameter values into corresponding digital signals, and level shifters for changing the voltage levels of signals indicative of such parameter values into a suitable predetermined level. On the other hand, the above output means include fuel injection valves arranged respectively at cylinders of the engine, an exhaust gas recirculating valve, and a fuel pump.
According to such abnormality detecting method, detection of abnormalities in the operations of such input means and output means is made in the following manners, as disclosed in Japanese Provisional Patent Publication (Kokai) No. 54-141926: To detect abnormalities in the functioning of the input means, it is determined whether or not the values of such parameter signals generated by the input means lie within respective ranges of values which can be obtained while the engine is normally operating. On the other hand, to detect abnormalities in the functioning of the output means, the amount of operation of the output means, for instance the valve lifting amount of any of the aforementioned valves, is detected, and it is then determined whether or not a signal indicative of the detected operating amount shows a value lying in a predetermined relationship with respect to the value of a command signal commanding the output means to achieve a required amount of operation, for instance, whether or not the difference between the value of the detected operating amount signal and the value of the command signal is larger than a predetermined value.
In the course of execution of such detection of abnormalities in the values of output parameter signals from such input means and in the values of actual operating amount signals from such output means, there can occur a phenomenon that the value of such a signal is wrongly determined to be abnormal due to an external disturbance such as noise, even when no abnormality actually exists in the input means or output means, resulting in unexpected execution of the aforementioned warning action and/or fail-safe action. To avoid such inconvenience, an abnormality detecting method has also been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 54-14634 corresponding to U.S. Pat. No. 4,246,566, which comprises detecting the occurrence of an abnormality in the value of each of the aforementioned parameter and operating amount signals available with input means and output means at predetermined intervals of time for instance, upon generation of each pulse of a signal indicative of top-dead-center positions (TDC) of the engine, resetting a corresponding one of abnormality determining timers provided for respective ones of the input means and output means each time no abnormality is detected in the signal value, while actuating the corresponding timer when an abnormality is detected in the signal value, and determining that the input means or output means is abnormal in functioning, after a predetermined period of time has elapsed from the last actuation of the corresponding timer. The above predetermined period of time is set at a suitable value dependent on the probable frequency of generation of noise in the parameter signal or the actual operating amount signal, or the required timing of execution of such warning action and/or failsafe action in the event of occurrence of an abnormality in the functioning of an input means or an output means to be diagnosed.
However, when an internal combustion engine is operating in a predetermined operating region, for instance, when the engine is in a starting condition wherein the starter of the engine is operating and simultaneously the engine rotational speed is lower than a predetermined value lower than the idling speed of the engine, for instance 400 rpm, most of the input means and output means are not yet in stably operable states. On such occasion, some of the output parameter signals or the actual operating parameter signals from the input means and output means can continuously show abnormal values over the respective predetermined periods of time of corresponding ones of the aforementioned timers. Further, at the start of the engine and when the engine is in an operating region immediately before stopping, wherein the engine rotational speed is lower than 20 rpm for instance, the time interval of generation of pulses of the aforementioned TDC signal can be larger than a predetermined counting period of time set for an abnormality determining timer as aforementioned. If on such occasion the timer is actuated due to noise or a like factor, the timer operates over its predetermined period of time before a resetting signal is applied to the timer to reset same. Consequently, it is wrongly diagnosed that the associated input means or output means is abnormal in functioning, resulting in unexpected execution of the warning action and/or fail-safe action.
Moreover, in a fuel injection control system for an internal combustion engine as disclosed in Japanese Provisional Patent Publication (Kokai) No. 54-141926, hereinbefore referred to, which is adapted to detect abnormalities in the functioning of the input means and output means, in synchronism with generation of pulses of an interrupt signal, if the abnormality detection is made in synchronism with generation of the TDC signal, when the engine is operating in a certain high rotational speed region wherein the time interval between adjacent pulses of the TDC signal is very small, only calculation of the fuel injection quantity, which is indispensable for control of the operation of the engine, is executed, while the abnormality detection of the input means and output means is suspended. If on such occasion an abnormality determining timer as aforementioned is actuated immediately before the suspension of the abnormality detection, the timer can continuously operate over its predetermined counting period of time, resulting in execution of the warning action and/or fail-safe action, because no resetting signal is applied to the timer after the suspension of the abnormality detection.